At present, in a Long Term Evolution (LTE) system, a pre-coding codebook is generally based upon Discrete Fourier Transform (DFT) vectors, and structured as a two-level codebook. Taking an 8-antenna codebook in Rel-12, a subset of DFT beam vectors is determined at a first level, and a User Equipment (UE) feeds an index of the subset of beam vectors among all of subsets of beam vectors, i.e., a Pre-coding Matrix Indicator 1 (PMI1), back to an eNB; and column selection is made at a second level from the subset of DFT beam vectors by selecting one or more columns from the subset, phase adjustment between polarization directions is made, and the UE feeds an index of the column selection and phase adjustment above among all of possible combinations (i.e., a PMI2) back to the eNB. The eNB generates, from the PMI1 and the PMI2 fed back at the two levels, a resulting pre-coding matrix for transmitting downlink data.
In the existing LTE system, the resolution of a codeword in a codebook generated as a result of column selection from a subset of DFT beam vectors is purely determined by the well defined DFT beam vectors, so the resolution can not be adjusted flexibly, thus degrading the performance of the system.